Final answer:
Activation of the medial hypothalamus may stimulate affective aggression through complex brain circuitry despite serotonin's inhibitory role, due to the involvement of the amygdala and interaction with other systems such as dopamine and stress response pathways.
Step-by-step explanation:
The question asks why affective aggression can be caused by activation of the medial hypothalamus, which sends axons to the serotonin-releasing periaqueductal gray (PAG), if aggression is inversely related to serotonin levels. The medial hypothalamus and the PAG are parts of the brain involved in the control of aggression, and their activation is thought to increase aggression despite the role of serotonin as an inhibitory neurotransmitter that may temper aggression. The key to understanding this paradox lies in the complex brain circuitry that regulates behavior. In particular, structures like the amygdala, which have a role in processing emotions, can influence the hypothalamus to initiate aggressive behaviors.
Activation of the amygdala can result in the stimulation of the fight-or-flight response via pathways including the medial forebrain bundle. The hypothalamus in turn regulates the release of stress hormones in response to emotional states. While serotonin generally inhibits aggression, other pathways or neurotransmitters could be involved in affective aggression, leading to complex interactions where the overall output is an increase in aggressive behavior despite the release of serotonin.
Serotonin does play a role in mood and cognition, but the relationship between neurotransmitters and behavior is not linear and involves multiple brain regions and mechanisms, such as dopamine pathways and stress hormone release. In particular, the coupling between serotonergic and dopaminergic systems and the impact of early life experiences on amygdala function can shape the way aggression is modulated in the brain.